The present invention relates to a stainless steel short fiber which is particularly suitable for use as a material of a filter for separating fine particles in a fluid and a process for the preparation thereof.
Hitherto, membrane filters have been known as a filter medium and, for instance, used for separating fine particles having a particle size of less than 5 .mu.m. These membrane filters have excellent characteristics such as being very thin, usually 50 .mu.m, and uniform in pore size, but have the disadvantage that heat resistance, solvent resistance and mechanical strength are poor due to an organic material. On the other hand, known filter mediums made of a metallic material, include a sintered compact of a powder obtained by atomization, chemical extraction or precipitation, and a sintered body of a relatively long metal fiber or filament. The former has the disadvantage that, since the porosity is small due to the shape of the powder being nearly spherical and also due to the need to maintain the efficiency for trapping contaminants and the mechanical strength, a certain degree of thickness is required and, therefore, the pressure loss of a fluid passing becomes relatively large. Also, the latter has the disadvantage that the pore size distribution is wide. A sintered metallic filter free from these disadvantages has been desired. The present inventor has attempted to prepare such a sintered metallic filter by employing other metal powders, fibers and filaments, e.g. powders obtained by mechanical pulverization using a ball mill, jetmizer mill and the like, but these materials also could not provide a satisfactory filter.
It is an object of the present invention to provide a novel material useful particularly as a filter material.
A further object of the present invention is to provide a stainless steel short fiber useful particularly as a filter material capable of forming a metallic filter having a high porosity, a narrow pore size distribution and excellent mechanical characteristics.
A still further object of the present invention is to provide a stainless steel short fiber capable of forming a metallic filter having characteristics like a membrane filter in spite of a metallic material.
Another object of the present invention is to provide a process for preparing a stainless steel short fiber suitable particularly for use as a filter material.
These and other objects of the present invention will become apparent from the description hereinafter.